The mammalian gaseous exchange system

• Structure of human gaseous exchange system

  A) ribs

  B) diaphragm

  C) alveoli

  D) bronchiole

  E) deoxygenated blood

  F) oxygenated blood

  G) intercostal muscles

  H) bronchioles

  I) bronchus

  J) trachea

  
• Structure and function - Trachea:

  1. Wide tube supported by incomplete rings of strong, flexible cartilage - Stop trachea from collapsing
  2. Incomplete cartilage rings - Food can move down oesophagus
  3. Goblet cells - Secrete mucus trapping microorganisms and dust
  4. Ciliated epithelium - Cilia beat and move mucus and trapped dirt away from lungs
• Trachea micrograph

  A) goblet cells

  B) cilia

  C) ciliated epithelium

  
• Structure and function - Bronchi / bronchus:

  1. Smaller rings of cartilage - Support
• Structure and function - Bronchioles:

  1. Walls of smooth muscle - Helps constriction and dilation changing amount air reaching lungs
  2. Lined with thin layer of flattened epithelium - Gaseous exchange is possible
• Structure and function - Alveoli:

  1. Elastic fibres - Stretch as air is drawn in and help squeeze air out aka. elastic recoil
  2. Large surface area - maximum diffusion
  3. Thin layers - Short diffusion distance
• Structure and function - Alveoli:

  1. Lung surfactant - Keeps alveoli inflated
  2. Good blood supply - Maintains steep concentration gradient
  3. Good ventilation - Steep diffusion gradient
• Arrangement of thorax:

  1. Rib cage - Semi-rigid case - Pressure can be lowered
  2. Diaphragm - broad, domed sheet of muscle, forms floor of thorax
  3. External and internal intercostal muscles - Between ribs
  4. Thorax lining - pleural membranes
• Process of inspiration:

  (Energy-using process)

  1. Diaphragm contracts, flattens and lowers
  2. External intercostal muscles contract - Ribs moved upwards and outwards
  3. Thorax volume increases - Pressure reduced (Lower than atmospheric air)
  4. Air drawn in
  5. Pressure equalised inside and outside
• Process of expiration:

  (Passive process)

  1. Diaphragm muscles relax - Move upwards to dome shape
  2. External intercostal muscles relax - Ribs move down and inwards
  3. Lungs return back to normal length - Volume of thorax decrease
  4. Pressure more than atmosphere
  5. Air moves out lungs until pressure is equal